First, off... /really/ love the diagrams. I gotta try out that software. I may draw mine just 'cause it looks so cool. I have some very similar stuff: 2020 AWD HR-Ext, dual alternators, dual truck batteries; ~8kWh of storage, Victron gear (Cerbo, MPPT, MultiPlus, Shunt), full-time connected "router" setup, and I'm using the truck charging the house batteries. IOW, silly over-kill stuff as many of our old-timers here will affirm. 😏
I've got a couple feedback items for you and a couple questions below, if you don't mind!
Hmm, good to know. I could probably fit 6x 100w panels and put them in series-parallel (three strings (in parallel) of two 100w panels in series).
my one question is from everything I’ve read, solar panels current is what changes with light levels, not voltage. So even in low light conditions, the voltages should still be above 18V?
Here's an example (from today) of 24V panel voltages (Cerbo GX is pretty sweet.) Left one is the battery voltage and the current being delivered by the panels (to the batteries). Right one is panel (controller input) voltage and current. "12V" panels would be half this.
So, yes, they start out ~16.5V (even when there's no current generated) and only climb to ~20V tops.
I know you've already made up your mind on 12V - and I see the logic of it on the DC storage / house simplicity side (the Victron 24V>12V DC converter is one of my weakest links); but I'd re-think the panel side. The panels are not 12V at any point - they require the MPPT (or PWM) to get them to the right voltage - and it doesn't matter what the input / panel voltage is, it's still 12V on the output side if that's what you want. I'm running 24V for both; but you can run 24V (or 48V) panel setup and still have 12V batteries - and it works better. That 6-gauge is suddenly just fine.
Also, change from 12V to 24V panels and you get twice the performance for the same cable sizes and the same Victron controller(s). That last part is important: some of the Victron MPPTs are 12/24/48 regardless of the amperage. So... buy the 50A unit you have planned to support ~600W of panels but it supports 2.4kW if you run 48V setup. Or change to the 30A and it supports ~720W at 24V. Easiest would be to just run all 24V panels; but you could do the series-parallel or whatever. And all still 12V on the storage / house side; you'd never see any difference from your planned setup - except it would work better on smaller gauge wire and you could buy a less expensive controller for 100% same performance.
On the panel setup, I bought 2 additional 50W panels to add to my 4 x 200W panels but ended up just not putting them on. The alternator charging is robust. I'd have been fine with 600W total. (And that might be what I have... I think one of the four panels isn't hooked up and I haven't opened it up to check.) You're welcome to the panels if you want them.
I found some CO2 / CO / smoke detectors that looked like they'd work with the Cerbo, but decided against it - I want them to be stand-alone. I also want them isolated from all the other power sources - though I haven't done that yet. I'll see if I can find links to what I'd found, though.
Water tanks and temp sensors work super well.
Can you point me to the analog propane sensor you found? I would LOVE to have that in the Cerbo. Using one of those silly Bluetooth app things now - works, but not as awesome as getting notification from the Cerbo.
Looking at the fuse plans, I changed to this Blue Sea fuse block
to save space. Only goes up to a 250A max, but useful with a lot of stuff versus external ANLs. Just more compact - used it in place of a positive bus-bar and fuses.
On the "Master Switch", I think the Blue Sea switches are 300A max. You might hit / exceed that (at 12V) depending on the inverter / charger / AC unit. Might need a separate master per battery?
(I know you know... but this is why 24V when doing large current.)
On the Sterlings, it looks like you're aware (and others have hinted) that you are unlikely to run two of those at full pull on the 175A fused CCP2. You could move to FPGA but I'm not sure that would even do it - can't recall limit but it's close.